The Electrical Tell Tale System for Trailers, Australian Patent No. 833898, and U.S. Pat. No. 6,535,113, is a device which monitors the electrical systems of trailers and communicates to the driver of a hauling vehicle if those trailer circuits are operating correctly or are malfunctioning. The Electrical Tell Tale System consists of a main control unit which is mounted at the rear of the vehicle and wired in series with each trailer circuit. From the main control unit is a modular cable which runs to the instrument panel of the vehicle and at this end of the cable is the tell tale monitor which houses a number of light emitting diodes. The light emitting diodes indicate to the driver whether the trailer circuits are functioning correctly.